I got an obdII code on 02 escort P0403. My 4th piston is misfiring. What would that be?

seems like a low oil problem but oil is full and no more than 2,000 miles old
Would the EGR possibly make my piston misfire? Because there may be definitly a noise coming from the piston area. Immediately it appears like in case you put a crushed up pop can in between your bike spokes.